Nonwoven fabrics, composed of unspun and unwoven fibers or filaments in which the fibers or filaments are adherently united to each other along at least certain portions of their length by means of an organic polymeric bonding agent, are a staple article of commerce. The base fabric may be an array of textile-length fibers, customarily of one to six inches in length, formed into a fleece or web by means of a card, garnett, air-lay device, or other web-forming device. Alternatively, the fabric may be composed of very short fibers, down to and including fibers of papermaking length, formed by known wet-lay or dry-lay processes, or the fabric may include textile-length fibers intermingled with papermaking fibers. Another category of nonwoven fabrics includes those formed from continuous filaments, extruded from spinerettes to form an unbonded or lightly bonded fleece. The present invention is applicable to all fibrous or filamentary arrays which are to be bonded to impart sufficient strength and integrity to the array to meet the requirements of the end use to which they are to be put.
Conventionally, the fibrous arrays are bonded by organic polymeric bonding agents in the form of aqueous dispersions or latices. Such polymeric latices are effective bonding agents, but they are often expensive compared with the cost of the fibers in the fabric, and they are for the most part flammable by nature when in the dry state as a component of a nonwoven fabric. Attempts have been made to add inorganic fillers to polymeric latices to decrease the cost of the bonding agent and to reduce the flammability, but effective loading with such fillers thickens the latex, while decreasing the tensile strength of the finished nonwoven fabric by an undesirable margin. Similarly, attempts to reduce the flammability of polymer-bonded nonwoven fabrics by treatment with flame-retardant finishes such as sulfamates, complex organophosphates, and the like, pose problems of irritation and potential toxicity.